Numerous systems are known in the prior art for providing an indication to vehicle operators that an emergency vehicle on call is nearby in order that the vehicle operators will be prepared for the sudden and unexpected appearance of the emergency vehicle at an intersection or otherwise in the traffic flow. Such systems often employ the broad approach of providing a low powered, special purpose transmitter in the emergency vehicle and suitable receiving equipment adapted to pick up the transmitted signal in the other vehicles if they are within range to provide an alarm indication to the vehicle operators. The present invention falls within this general class and is directed particularly to the provision of a more effective operator alerting technique and apparatus within the receiving vehicles.